A number of devices, software applications, websites, and the like require authentication of a user before granting access. For example, Completely Automated Public Turing Tests to Tell Computers and Humans Apart (CAPTCHA) techniques may be used for authenticating that a human user is not a machine or computer when attempting to access devices or various on-line environments. A user may be required to pass a CAPTCHA test to access a device, access a website or webpage, access an application, buy tickets to an event, enter a comment on a blog, create an email account, or the like.
CAPTCHA techniques may become ineffective, for example, due to object character recognition (OCR) technologies becoming better at deciphering text of graphic CAPTCHAs, the difficulty of making sense of modified graphical characters on a display (especially in bright sunlight), the difficulty of discerning words of an audio CAPTCHA in view of background noise or user hearing impairments, and the like. By having more advanced CAPTCHA techniques, authentication of a user may become more user-friendly and also more resistant to unauthorized access by a machine or computer.